Piezo electric oscillation generator



Feb. 19, 1935. "H. MEAHL PIEZO ELECTRIC OSCILLATION GENERATOR Filed Oct. 15; 1951 Inventor:

Harry R. meahl,

H is Attorney.

Patented Feb. 19, 1935 1 1 I I I U ITED STATES PATENT OFFICE i v 1,992,035

General Electric Company, a corporation of New York Application October 15, 1931, Serial No. 569,000

6 Claims. (01. 250-36) My invention relates. to oscillation generators anode and cathode of the discharge device may of the type in which the frequency is controlled be supplied to any desired load circuit. In the by means of a piezo electric device, such as a drawing I have indicated by the rectangle 12 the quartz crystal. amplification stages of an ordinary radio trans- It has for one of its objects to provide an osmitter by means of which oscillations from the 5 cillation generator of the type indicated in which anode 1 are amplified and supplied to an anthe frequency of oscillations produced is affected tenna 13. to a smaller degree by circuit adjustments and i As thus far described the system of my invenextraneous influences than has heretofore been tion is similar to that described in Fig. 3 of practicable. i United States Patent No. 1,472,583 to Walter G. 10

A further object of my invention is to provide Cady, issued October 30, 1923. I have found, an oscillation generator of the type indicated however, that very pronounced improvements in which is characterized by improved constancy of the operation of the system may be effected by frequency of oscillations produced and which at tuning the circuit 5, 6 to a frequency within a 15 the same time, when using an electron discharge range of from one quarter to three quarters or 15 device of a particular rating, is capable of prothe crystal frequency and by so connecting the ducing a greater amount of high frequency entransformer 5, 8 that oscillations are supplied ergy in the output circuit than has heretofore from the anode circuit to the grid circuit in debeen possible. generative phase; that is, in such phase that were Still afurther object of my invention is to pTothe grid connected directly to the upper termi 20 vide a piezo electric oscillation generator utiliz- 119.1 of winding 5, or were the crystal 4 removed ing a three electrode electron discharge device from the circuit, the system could not oscillate by and in which extremely high anode'voltage may virtue of the coupling between the anode and be employed without subjecting the crystal to grid circuits. The electromotive force supplied to stresses likelyto cause rupture thereof. the grid circuit by the inductive effect between 25 The novel features which I believe to be charwindings 8 and 5 then opposes that supplied to acteristic of my invention are set forth with parthe grid due to the inherent capacity effect exticularity in the appended claims. My invention isting between these windings and between the itself, however, both as to its organization and grid and anode of the discharge device, thereby method of operation, together with further obleaving onlya residual of energy transfer sufli- 3o jects and advantages thereof, may best be under cient to support oscillations when the crystal is stood by reference to the following description in place, taken in connection with the p nyi It has been found that with the system as thus. drawing in Which Fig. 1 epresents an embodi. adjusted-oscillations of high power are produced m f y invention and Fi 2 pr s nts a in the output circuit having the natural fre- 3 modification thereof. quency of the crystal and further that the fre- Referring the wing, I have'shown in Fig. quency of these oscillations is unaffected by 1 an electron discharge dev having an anode 1, circuit adjustments over a very large range therea 2, a cathode 3 Between gridand of Thus for example the frequency remains 40 cathode is connected a piezo electricdevice 4 in b t ntially t t, ver the range of adjust-I Series with a'tuned circuit comprising inductanqe ments'of circuit 5, 6 for resonance at any fre 5 and a condenserfi. The piezoelectric device 1s quency within the range between approximately shuntgd by i m fthelsual g 3 one quarter to three quarters of the crystal fre-ja passage m e Curran an quency. With the circuit tuned within this t establish a ro er bias u on the grid. The

i ductance 5 of th e tuned ci rcuit comprises the range I a fqund no condltlon under Whlch the secondary winding of a step down transformer system W111 osclnate at any frequencyother than the primary winding 8 of which is connected'bethe natural freqilency of the crystelvIf the tween the anode and cathode of thedischarge ing of the circult Varied from the neighbor? device'in series with a source of anode potential hood of three quarters of the natural frequency 50 9. If desired, a choke coil loconnected in series of the crystal toward the crystal frequency,v oswith the source 9 and a by-pass condenser 11 cillations cease until a point is reached at which connected. in shunt therewith may be employed the circuit is tuned to a frequency substantially to prevent the flow of high frequency currents in equal to, or slightly higher than the crystal frethe battery'9. Oscillations produced between the quency where oscillations are again produced 55 grid and anode of the discharge device employed, the crystal being connected between the grid and cathode. As thus constructed the system operates solely by virtue of the inherent coupling between the anode and grid within the discharge device.

In the system of my invention, on the other hand, the oscillations are produced solely by virtue of the close coupling which exists between the coils 5 and 8. It has been found that if this coupling be removed, or winding 5 short-circuited, oscillations immediately cease. This is true even though the primary winding 8 has a natural period greater than the crystal frequency. The inherent capacity between the anode and grid of the system constructed in accordance with my invention has but slight effect in supporting operation of the system, and may be eliminated, as by the use of a discharge device of the screen grid type in which the screen grid is maintained at positive potential and is grounded by means of a condenser to the cathode, without adversely affecting the operation of the system. I have found, however, that a slightly different adjust ment of coils 8 and 5 may be necessarywhen a screen grid tube is employed.

A further important advantage resulting from my invention resides in the fact that extremely high anode voltages may be employed without subjecting the crystal to stresses likely to cause rupture thereof. It has been customary in pieso electrically controlled electron discharge oscillators of the prior art to employ an anodevoltage upon the. discharge device which is a relatively small portion, 'as for example, less than half, of the maximum rated anode voltage of the discharge device. This was necessary in order to secure desired stability of operation of the system under control of the crystal and to protect the crystal against excessive stresses. It has been found, however, that with the circuit arranged as herein described a value of anode voltage approximately equal to or slightly less than the maximum rated anode voltage of the discharge device may be employed without reducing the stability beyond that which is obtainable from the best circuits of the prior art when using about one-half of the maximum rated anode voltage. For a specifieexample, when utilizing a particular discharge device known inv the art as UX 210 an anode voltage of four hundred volts may be utilized without subjecting the crystal to dangerous stre'ss'whereas when this discharge device is employed in the circuits of the prior art it is im practical to utilizea value of anode voltage in excess of approximately one-half of this amount.

For a test of my device under practical opera'ting conditions it was connected to control the frequency -of a hi h power broadcast transmitter operating in actual service at a frequency of 790 kilocycles. It was in continuous service for a period of about a month during which time the maximum frequency drift from normal which occurred was '7 cycles and the average frequency drift was 4.6 cycles. An oscillation generator of the fixed tuned anode typereferredto abovein which the capacity between the grid and anode was relied upon for operation of the device employed in the transmitter and under the same operating conditions, including the same discharge device and the same values of operating voltages, for a period of a month produced a. maximum frequency drift from normal of 90 cycles and amean frequency drift of 35 cycles. In this test the anode voltage employed was of a value appropriate to the latter type of circuit. Even under this condition the output obtained from the circuit in accordance with my invention was approximately one and one-half times greater than thatobtained from the prior art circuit during the entire period in which the system was in operation. 1

In Fig. 2 I have shown a modification of the arrangement shown in Fig. 1 whereby additional advantages are obtained. In this Figure I have shown a resistance 14 connected in series with the anode circuit of the discharge device and having a condenser 15 variably connected across a portion thereof thereby to permit of vuiatim of the alternating current resistance of them circuit. Thisis desirable in'the event that the impedance of the input to the transform 8, 5,-

as due for example to di's'tributedcapazity in the winding 8, is lowas compared with the anodeimpedance of the. discharge device at the frequmcy at which the system operates. In this case all; alternating current resistanceof the anode circuit should be of such value asto cause"tthe external impedance of the anode circuit approximately to match, or, in the case of arlow impedance tube, to exceed, the internal anode impedance of the discharge device. In cases where the system is designed for operation at a shade frequency the resistance .14 may be omitted and the coil 8, 5 designed to afford the desired, pedance, but where the system is operated over a range of frequencies it is "usually desirable that the resistance be employed to hold the impedance of the anode circuit up ,toa desired value at those frequencies where the impedance of the coil is too low for efficient operation of the discharge device. I

This resistance. has the effect of increasing the range of circuit adjustments over which desired operation of the device under control of the crystal may be had. It has been found that with re sistance 14 properly adjusted oscillations having the frequency of the crystal are produced Over a range of adjustment of the circuit 5, 6 for resonance at frequencies varying from one 'quarter of the crystal frequency to the crystal 'frequencytnd even slightly higher than the crystal dependent upon the activity of the partictflar crystal used. The frequency at which the circuit 5, 6 is tuned for best operation of the system, however, variessomewhat with the natmal frequency of the crystal. For example, a crystal having a natural frequency of 1928315 lac. was found to produce best operation when circuit was tuned to af-requency about 94% of the crystal frequency whereas a. crystal having a natural frequency of 4750-kc. was found to arm duce best operation with the grid circuit tuned at about 72% of the crystal frcquencywczystals having intermediate natural frequencies were Hi0 found to produce best operation with the grid circuit tuned at intermediate percentages of. the crystal frequency. Thus for bestyopera-flonihe percentage of the crystal frequency atwhichgjhe circuit 5, 6 should be tuned decreases atthecryee tal frequency increases. At vexylowdmm I as for example, with a crystal of kc. frequency the circuit 5, 6 may be tuned relatively close, as for example within 1 percent, to the crystal frequency. I attribute this result principally to the increasing effect of extraneous influences upon operation of the system at the higher frequencies and increased activity of high frequency crystals.

It will also be observed in Fig. 2 that the crystal 4 is connected between the tuned circuit 5, 6 and the cathode. This is important in that the crystal cell may be grounded thereby avoiding the necessity for insulation of the crystal cell from ground. Further the necessity for isolation of the cell from ground to avoid certain undesired capacity effects are avoided.

The resistance 7 in this figure isconnected directly between the grid and cathode.

While I have shown a particular embodiment of my invention it will of course be understood that I do not Wish to be limited thereto since difierent modifications in the arrangement employed may be made and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. The combination, in an oscillation generator, of an electron discharge device having a grid, an anode, and a cathode, a transformer having a primary winding connectedbetween the anode and cathode, and a secondary winding connected between said grid and cathode, a piezo electric device connected in circuit with said grid and said secondary winding, said winding being so poled that the voltage on the terminal thereof connected to said grid is in degenerative phase when the piezo electric device is removed from said circuit, and means whereby said transformer is tuned to a frequency substantially lower than the natural frequency of said piezo electric device during the operation of said oscillation generator to produce oscillations having said natural frequency.

2. The combination, in an oscillation generator, of an electron discharge device having a grid, an anode and a cathode, means to cause said discharge device to produce oscillations, said means including circuit connections between the grid and cathode and anode and cathode, an inductive coupling between said circuit connections, a piezo electric device coupled with said circuit connections to control the frequency of said oscillations, and means includes said inductive coupling to reduce the reaction on said piezo electric device to such an extent that oscillations having the natural frequency of said piezo electric device are produced over a range of tuning of said circuit connections extending from the crystal frequency to a frequency less than half of the crystal frequency, and means to tune said circuit connections to a desired frequency in said range.

3. The combination. in an oscillation generthe discharge device.

4. The combination, in an oscillation generator, of an electron discharge device having an anode, a cathode, and a grid, a tuned circuit and a piezo electric device connected in series between said cathode and'grid, a source of electromotive force connected in circuit between said anode and cathode and an inductive coupling device having its input connected in circuit between said anode and cathode and its output connected in circuit between the grid and cathode, said coupling device being poled to supply oscillations from the anode circuit to said tuned circuit in degenerative phase and to protect said piezo electric device against the anode voltages whereby said source of electromotive force may have a value approaching the maximum rated anode voltage of said discharge device without endangering said piezo electric device.

5. The combination, in an oscillation generator, of an electron discharge device having a grid,

an anode, and a cathode, a transformer having a primary winding connected between the anode and cathode, and asecondary winding connected between the grid and cathode and a piezo electric device connected in series circuit relation with said grid and said secondary winding, means to tune said secondary winding, the tuning of said grid circuit being determined by said means, said windings being so poled that the voltage induced in said secondary winding due to mutual inductance between said windings is supplied to said grid in opposition to the voltage-supplied to said grid due to capacitive effects between said windings.

6. The combination, in an oscillation generator, of an electron discharge device having an anode circuit and a grid circuit, a transformer having an untuned primary winding connected in said anode circuit and a tuned secondary winding connected in said grid circuit, said windings being so poled that the electromotive force supplied to said grid circuit due to mutual inductance between said windings is opposed to electromotive force supplied to said grid due to capacitive effects between said windings, and a piezo electric device connected in series with said tuned secondary winding and said grid, said transformer being so proportioned that said electron discharge device is inoperative to produce oscillations except when said piezo electro device is connected to said grid HARRY R. MEAHL. 

